Electrographic print-head having an image-defining multisegmented control electrode



April 8, 1969 R. s. HOWELL 3,433.053

'ELECTROGRAPHIC PRINT-HEAD HAVING AN IMAGE-DEFINING v l MULTISEGMENTED CONTROL ELECTRODE Filed July 20, 1964' Sheet of2 INITIATING PULSE SOURCE 1 CONTROL V VOLTAGE .w

SOURCE INVENTOR.

. RICHARD S HOWELL April 8, 1969 R. s. HOWELL 3, 38,053 ELECTROGRAPHIC PRINT-HEAD HAVING AN IMAGE-DEFINING MULTI'SEGMENTED CONTROL ELECTRODE Filed July 20,1964 Sheet z of2 SPOTDIAMETERGUN MILS) 0 '10 6 0 5p 4 o 5 0 29 up 9 1p 2p 50 4p 59 6 0 7p 20o f -400- f l g 600" Lg E --1000 E o I g -|200 i' Q l FIG.4

INVENTOR. RICHARD S. HOWELL United States Patent US. Cl. 346-74 2 Claims ABSTRACT OF THE DISCLOSURE An electrographic apparatus for depositing upon a charge retentive medium a latent image of controllable size and shape produced by ions discharged from coaxially arranged electrodes; the shape and size of said image is dependent upon an electrical bias on a control electrode in the ion path and the physical shape and size of an aperture opening in the control electrode and the thickness of the control electrode.

This invention relates to apparatus for depositing a charged image on a recording medium, and more particularly to an electrographic print station for depositing a charged image of controllable magnitude upon a chargeretentive medium.

In copending application S.N. 729,847, filed Apr. 21, 1958, now US. Patent No. 3,195,142, entitled, Electrographic Recording Process and Apparatus, by Robert E. Benn and Richard S. Sakurai, which patent is assigned to the assignee of this application, an improved apparatus for depositing a charge on a recording medium is described. A print head is provided having a 5 x 7 matrix of pin-shaped print electrodes. A closely spaced initiating electrode, also pin-shaped, is provided for each of the print electrodes. The print head has a planar print face in which the print and initiating electrodes terminate. A planar back electrode is located at a distance from and substantially parallel to the print face.

Means are provided to apply a print voltage pulse to a print electrode. The print pulse establishes a unidirectional divergent electric field between the print electrode and the back electrode. While the intensity of this field is of sufficient value to sustain ionization within the gap between print and back electrodes, once electrically charged particles have been introduced into that gap, the field is insufficient to cause the initiation of such particles.

Such particles are introduced into the gap by an initiating pulse applied to the initiating electrode associated with the energized print electrode. Simultaneous app1ication of a print pulse and an initiating pulse to associated initiating and print electrodes causes a disruptive discharge to occur between those electrodes.

The discharge introduces a large number of charged particles into the gap. The unidirectional electric field, which exists between the print electrode and back electrode, causes propagation of a stream of charged particles across the gap and the establishment of a charged area on the surface of a record medium located between the back electrode and the print head print face.

An advantage of the above system over previous techniques, wherein only a single electrode was used in the print head for both initiating and maintaining a discharge, is that since the voltage necessary to maintain discharge is less than that required to initiate one, the voltage that is required to be maintained between the print electrode and the back electrode is considerably lower where an initiating electrode is employed.

In certain applications, it is desirable to have control over the size of the charged spot deposited on the recording medium. This has been possible with the print head-s just described by varying parameters such as the gap between the record medium and the print face of the print head. However, this parameter may not be readily variable in operation.

Accordingly, it is an object of this invention to provide an improved electrographic print head.

It is another object of this invention to provide an electrographic print station wherein the magnitude of an individual charged area may be readily controlled.

It is a further object of this invention to provide an electrognaphic print station wherein the magnitude of a charged image may be altered over a wide range by the adjustment of a bias voltage.

A still further object of this invention is to provide an electrographic printing station incorporating a printing head and comprising a segmented control grid capable of modifying the field followed by a stream of ions to readily provide required shapes and sizes of charged indicia symbols created by depositing the stream of ions upon a recording medium.

These and other objects are achieved by the addition of an apertured control electrode to a print station of the type having a print head with one or more electrodes terminating at its face. Each print head electrode set is preferably coaxial, the central pin serving as an initiating electrode, the outer cylinder serving as a print electrode. An ion stream, established between a print head electrode and a back electrode, located behind the recording medium, passes through an aperture in the control electrode. A control voltage is applied to the control electrode. The shape of the ion stream and the size of the charged spot it creates upon the record medium may be readily controlled by manipulating the electrostatic field in the aperture through adjustment of the control voltage.

While some of the objects and a brief description of the invention have been given above, the invention and its objects will be best understood by referring to the following detailed descriptions and to the accompanying drawings wherein:

FIG. 1 is an isometric view, partially broken away, of a preferred embodiment of a print station incorporating the control electrode.

FIG. 2 is a cross section of FIG. 1 taken along the lines 2-2 and showing, in addition, in block and schematic form, the arrangement of voltage supplying circuits and sources used to operate the print station.

FIG. 3 is a graph of spot size as a function of control voltage.

FIG. 4 is a fragmentary pictorial and schematic plan view of another embodiment of the invention employing a segmented control electrode.

Referring to FIG. 1, there is shown print head 11 having a substantially planar print face 13 and an array of print head electrode sets 15 terminating in the print face. Resting next to the print face 13 is control electrode 17. The control electrode is of conductive or serniconductive material and has an array of apertures 18 corresponding to the print head electrode sets 15 in the head. The apertures are concentric with the print head electrode sets 15. A planar, back electrode 19 is located in a spaced-apart relationship with the control electrode and substantially parallel to it. Record medium 21 is located between the control electrode 17 and the back electrode 19.

FIG. 2 illustrates the arrangement in more detail. Each print head electrode set 15, embedded in the print head 11, is coaxial and comprises a central pin 23 which functions as the initiating electrode, and a cylindrical electrode 25 which functions as a print electrode. The initiating,

central electrode 23 is separated from the print electrode 25 by insulating layer 27.

Back electrode 19 is tied to some reference potential, which may be electrical ground. Print electrode 25 is maintained at potential V by print voltage source 29. Initiating electrode 23 is connected through resistor 31 and secondary winding 33 of transformer 35 to print voltage source 29. The primary winding 37 of transformer 35 is connected to initiating pulse source 39.

Upon energization of initiating pulse source 39, initiating voltage pulse V appears across initiating electrode 23 and print electrode 25. This voltage is of a sufficient magnitude to cause a disruptive discharge 41 to occur between the electrodes 23 and 25. Resistor 31 is primarily a currentlimiting resistor. Depending upon the polarity of the print voltage V positive or negative ions in the form of a stream 43 are propagated toward the recording medium 21, depositing a charged spot 45 on it.

Control voltage V is applied to control electrode 17 by control voltage source 47. The control voltage V may be of the same polarity as the ions in the stream 43, in which event, the electrostatic field created within the aperture 18 by the control voltage V will have a constricting effect on the ion stream, tending to reduce spot size G. Conversely, the control voltage V may differ in polarity from that of ions in the ion stream 43, in whichevent,

the electrostatic field within the aperture 18 will tend to enlarge the crosssectional size of the stream 43. When the ions in the stream and the control voltage V have opposite polarities, an increase in the control voltage will result in an increase in the size G of the charged spot 45.

While in no wise to be construed as limiting the scope of this invention to such values of parameters, the following figures are those used in a model which was built to incorporate the features shown in FIG. 2.

Initiating pin diameter A mils 5 Spark gap B do 3 Control electrode aperture diameter D do Control electrode thickness E do 30 Control electrode-to-print medium spacing F do 20 Spot diameter G do .0 to75 Print voltage V volts l,000 Control voltage V do -500 to -l,500 Initiating voltage V; do 1,30O Resistor 31 ohms 300K Duration of voltage V; microsec 40 The spot size G resulting from the above paramters may best be observed by referring to FIG. 3 wherein spot size G is plotted against control voltage V for three different control electrode thicknesses E. It may be seen that spot diameter G is an almost linear function of control voltage V with an increasing control voltage resulting in diminished spot size. This occurs since the greater the negative control voltage V the larger the constricting effect it has upon the ion stream 43 passing therethrough.

Similarly, it may be observed that for a given control voltage V spot size G may be diminished by increasing the control electrode thickness E. This follows, since, with a thicker electrode, constriction or expansion, in accordance with polarity of the control voltage, of the ion stream 43 is effected over a longer portion of the total path of the ion stream 43 to the recording medium.

Similarly, dimensions other than the control electrode thickness B may also be changed. Control electrode aperture diameter D, for example, may be reduced where a smaller range of spot diameters G is desired. Control electrode-to-print medium spacing F is noncritical, and may be changed without altering operation of the print head.

While in the illustration given above, the apertures 18 used were shown to be circular, this need not necessarily be so; for example, where a large number of closely spaced electrode pins are used in the print head, a row of such electrodes may have a common, slot-shaped aperture rather than individual circular apertures in the control electrode where elliptical-shaped spots are desirable. Likewise, the electrode 17 need not be a single plate, but may be individual to each pin, and may be an integral part of the head itself.

Referring to FIG. 4, an embodiment is provided which affords greater flexibility and control over the shapes of the areas of charge deposited on the record medium. In this embodiment, the control electrode 17 is divided into segments 60. Four segments are shown in each section or group (not numbered) of control electrode 17 but more or less than four segments, and in various configurations, could be employed. The segments 60 are electrically insulated from each other by air pockets or electrical insulation 61. Where semiconducti-ve material is used for the control electrode, junctions could be formed to provide the required insulating barriers between segments.

Individual sources of voltages, shown as V V V V and V V Vet, V08, are electrically connected to the segments 60 of the sections of control electrode 17. Thus, different voltages may be applied to each segment 60. Additionally, corresponding segments 60 of each section of control electrode 17 may be connected to a common voltage source; for example, a left segment of each section might be connected to source B and a right segment of each section might be connected to source B Alternatively, some of the segments 60 may be grounded or may be left floating.

Voltage sources may be switched to different segments 60 for varying the combination of voltages applied to the segments 60.

Varying the voltages applied to the control electrode segments 69 varies the configuration of the electrostatic field around the ion beam and hence, migration of the ions to the recording medium is correspondingly affected so as to provide the desired shape and size of the discharges of ions upon the recording medium.

The use of the control electrode described above need not be confined to print stations employing a coaxial pin type print head. To the contrary, such an electrode may also be employed with the double pin arrangement described in the Benn-Sakurai patent previously referred to. Additionally, the control electrode may also he employed with the pin-bar arrangement disclosed in US. Patent No. 3,068,479, of Robert E. Benn, Richard S. Howell, and Richard S. Sakurai, entitled Electrographi c Recording Apparatus and assigned to the assignce of this application. In both cases, the apertures of the control electrode will be located opposite the point in the prmt face where the ion stream originates. In the case of the Benn-Sakurai application, this may be some point 1ntermediate the pair of initiating and print electrodes. In case of the Patent No. 3,068,479, this point may be between the initiating pin electrode and its associated print bar electrode.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced other than as specifically described and illustrated.

What is claimed is:

1. In an electrographic print head having coaxially arranged electrodes for depositing upon a record medium supported by a back electrode connected to a reference potential a charged image by means of an ion stream between said print head and said back electrode, the improvement comprising in combination,

a control electrode substantially surrounding said ion stream and comprising segments arranged to form an aperture through which said ion stream passes, said segments being of a particular thickness and relatively electrically insulated from one another,

means for applying individual voltage bias to each of said segments for controlling the size and shape of said charged image and means for individually varying the electrical bias of each of said segments.

2. An electrographic print head having a substantially planar print face and an array of sets of coaxial electrodes terminating at said face for depositing charged images upon a record medium resting upon a grounded electrode, comprising:

means for generating and, in cooperation with said grounded electrode, for propelling ion streams to impinge upon said record medium;

a control electrode comprising groups of segments of selectable thicknesses, each group arranged to form an aperture through which one of said ion streams passes and each group substantially concentric with one of the sets of coaxial electrodes, and

means for biasing said segments at selected voltages in combination with the selected thickness of the segments of the control electrode, for aifecting substantially linearly the shape and size of said charged images.

References Cited UNITED STATES PATENTS Roche 313-138 Meston.

Selenyi.

Smits.

McNaney.

Benn.

Byrd.

Glaser 250-49.5 Kuehler 34674 Po Lee 34674 Epstein 34674 US. Cl. X.R. 

